Working machines of the type where an internal combustion engine drives a working unit and an electric motor drives traveling units are known, for example, from Japanese Patent Application Laid-open Publication No. 2001-271317. The conventional working machine disclosed in the No. 2001-271317 publication will be outlined below with reference to FIG. 14.
In FIG. 14, the working machine 300 is constructed as a snow plow or snow removing machine including a machine body 301, on which are provided: a working unit 304 including an auger 302 and blower 303; an engine 305 for driving the working unit 304; left and right traveling units 306 each including a crawler; left and right motors 307 for driving the traveling units 306; a power generator 309 driven by the engine 305 for supplying electric power to a battery 308 and motors 307; and a control 311 for controlling the motors 307 etc. The power generator 309 is driven by a portion of the output of the engine 305, and electric power thus produced by the generator 309 is supplied to the battery 308 and motors 307. The remaining portion of the output of the engine 305 is supplied via an electromagnetic clutch 312 to the working unit 304 for rotation of the working unit 304. In this way, the working machine 300, constructed as a snow removing machine, drives the working unit 304 via the engine 305 and drives the traveling units 306 via the motors 307.
Because the working unit 304 and traveling units 306 are driven via the engine 305 and motors 307, respectively, the battery 308 is often of a relatively small capacity and small size; the battery 308 need not have a large capacity since electric power can be constantly supplied by the generator 309 driven by the engine 305. Namely, it is only necessary for the generator 309 to generate an amount of electric power slightly greater than that consumed by the motors 307.
With such a working machine 300, a user or human operator sometimes wants to cause the machine 300 to temporarily travel a short distance with the engine 305 kept deactivated, such as when the machine 300 is to be moved in or out of a storage space or transferred from the storage space to a nearby working place. It would be very cumbersome to activate the engine 305 on each of such occasions. Further, since the motors 307 are driven only by the power supplied from the small-capacity battery 308, a great amount of electric power would be consumed from the battery 308. Therefore, the working machine 300 can travel for only a limited time, and a further improvement has to be made in this respect. Further, if the remaining capacity of the battery 308 is reduced excessively, then the engine 305 can not be activated by the power supplied from the battery 308; besides, the battery 308 can not be charged appropriately by driving of the engine 305. In addition, the over-discharge of the battery 308 would adversely influence the performance and life of the battery, and a further improvement has to be made in this respect too.